Method of cracking hydrocarbons



J. H. SHAPLEIGH METHOD OF CRACKING HYDROCARBONS Sept. 15, 1959 3 SheeLs-Sheefl l Filed Feb. 19, 1954 JAMES H. SHAPLEIGH INVENTOR.

AGENT.

Sept. 15, 1959 J. H. sHAPLElGH 2,904,502

METHOD oF CRACKING HYDRocARBoNs Filed, Feb. 19, 1954 3 sheets-sheet La Sept. 15, 1959 J. H. sHAPLElGH METHOD oF .CRACKING HYDRoCARBoNs Filed Feb. 19, 1954 3 Sheets-Sheet 3 JAMES H. SHAPLEIGH INVENTOR.

AGENT.

2,904,502 Patented Sept. 15, 1959 United States Patent Office METHOD F CRACKING HYDROCRBNS James H. Shapleigh, Wilmington, Del., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Application February '19, i954, Serial No. 411,378

13 Claims. (Cl. 208-130) This invention relates to the cracking of hydrocarbons and more particularly to a process for the thermal cracking of normally liquid hydrocarbons in a tubular furnace to produce oils or liquids containing compounds of the same or different chemical series from those treated and more p-articularly to produce modified mixtures of compounds valuable as intermediate and end products.

In Reissue Patent No. 21,521, there is disclosed a process for treating hydrocarbons in a tubular furnace fired at a plurality of spaced points to give flexible temperature control of the reacting fluids. Additionally, in Patent No. 2,525,276, there lis disclosed a process for the cracking of hydrocarbon oils with a minimum of carbon deposition for the substantial production of olefins. These patented processes heretofore set forth have provided practical flexible processes for hydrogen production and the cracking of whole oils to produce valuable liquid components as well as olefins through reaction control. However, in so far as it `is known, no process has been developed which utilizes externally heated metal tubes and affords a yield of cracked products and throughput which is attractive to large-scale handling of hydrocarbon stock such as is encountered in the reiining of petroleum.

In the art of oil rening, the large plants which now exist are the result of years of progress wherein one of the principal objectives has been economy in the production of refinery products. To achieve this end, extensive processing technique has been employed in the majority of instances to preprocess feed stocks, and to cyclically move large bodies of catalyst. These techniques,though great in undertaking, have certain elemental features. The starting point is an oil which can be principally represented by a carbon-hydrogen relationship. Por example, as approximately CH1 85 for an East Texas crude, or as CHL@ for another crude; but whether crude, distillate or residue, a single carbon-hydrogen relationship can be used to express the initial stocks, intermediates, and end products notwithstanding that they are mixtures of hydrocarbons.

In the art of oil refining, it is not customary t0 deal in the foregoing terms, but rather to deal with cuts and distillates, boiling points, and other factors which in general characterize the physical properties of the material.

In contrast, in tubular high temperature cracking it has been discovered that composite products, expressed in terms of carbon and hydrogen, follow a relationship directly influenced by the process conditions peculiar to this invention, and whereby the heat input` per tube is brought to a previously thought impossible high value which expressed in refinery terms of throughput is inthe order of, for example, for a one-tube unit of 50 to 150 barrels offeed stock per day; or for a nominal size 100 tube installation of 5000 to 15,000 barrels of feed stock per day.

Utilizing the carbon-hydrogen.terminology referred to above, the refinery `for example may start with a feed stock CH1.8 The refinery does two basic` things to the stock: v(l) applies heat, and (2A)` provides a residence utilize substantial sized heat exchangers prior to entering the residence chamber or reactor. Another procedure is to heatflarge amounts of catalyst while in cyclic movement. In other procedures, noncatalytic type stills are used. The physical aspects are, however, the same, whether catalytic or noncatalytic, i.e., to supply heat and residence time. In the supply of bulk heat according to the procedures heretofore set forth there is a fundamental deficiency in lack of control, regardless of the elaborate instrumentation 4employed with installations now in existence. For example, the moving bed of catalyst `is hottest at its entrance point and follows a descending gradient o f temperature during its residence time path. The conditions of limited body temperature and 'bulk solids move.- ment coat the catalyst with carbon even when handling light distillate, for example, in the form of vaporized gas oil and are prohibitive for heavy stock within reasonable carbon limits. The carbon-coated catalyst must be removed from the reactor, burned free of carbon and recycled.

In contrast, it has been discovered that high throughput is obtainable in tubular cracking in similar terms to those of refinery practice under conditions of much improved control and flexibility. Where catalytic operation is desired, the invention permits carbon formation to be greatly minimized, and permits its relatively easy removal without physical disturbance of the catalytic bed; or if desired, bed movement can still be employed as an alternative while retaining certain advantages. It is preferred, for example, that catalyst, if used, be in a layer parallel to the tube surface, and preferably forming or being part of a radiantly heated internal core within the tube. So used, the catalyst surface is normally at a temperature which promotes reaction to generally cause a decarbonizing state, while at the same time the catalytic action can proceed at an abnormally high rate per unit of surface.

Accordingly, it is a principal object of this invention to secure desired cracked products under conditions of high throughput and under conditions where the fundamental deficiencies heretofore set forth are eliminated. Other objects of the invention will appear hereinafter, the novel features and combinations being set forth in the appended claims.

More specifically, the objects hereinbefore and hereinafter set forth are achieved in accordance with this invention by the improvement which comprises passing hydrocarbon and diluent gas through the reaction zone of an elongated reaction tube for a period of not more than 0.3 second residence time in the reaction zone of the tube, said tube being disposed within a refractory walled furnace having an average surface temperature of at least 1835 F. in the reaction zone and supplying external heat to the tube from the refractory walled furnace to maintain a temperature relationship within the reaction zone between the average surface temperature of the furnace wall and the average temperature of the reaction tube of at least F. and to maintain within said reaction zone a temperature relationship between the average temperature of the said tube and the temperature of the cracked products emerging therefrom of at least 435 F.

Certain embodiments of the invention are presented herein for the purpose of illustration but it will, of course, be understood that the invention is susceptible to different modiied embodiments which come within the scope of the appended claims.

Inthe accompanying drawings:

Fig. 1 represents diagrammatically a flow chart with suitable equipment for carrying the invention in-to effect;

Fig. 2 is a schematic sectional view showing an alternative Iembodiment for proving a fixed catalytic surface for the reaction equipment illustrated in Eig. 1; and

Fig. 3 is a schematic sectional view showing still another embodiment for providing a movable catalytic surface for the reaction equipment illustrated in Fig. 1.

Fig. 4 is a schematic sectional view showing still `another embodiment for providing a uidized catalytic body for the reaction equipment illustrated in Fig. 1.

Fig. is a schematic sectional view showing still an.- other embodiment for providing an effective application of countercurrent diluent for the reaction equipment illustrated in Fig. 1.

Referring to Fig. 1, feed oil is passed through a line 1 into and through a pump 2 from which it is passed by a line 3 into a preheater 4. From the preheater 4, the oil is passed through a valved line 5 into a mixer 6. Primary steam from valved line 7 is admitted to the mixer 6 wherein the oil is atomized and partially vaporized and is passed into an injection tube S. The injection tube S extends into a reaction tube 9 which extends through a refractory walled furnace 10 which is preferably fired at a plurality of spaced points. Within the reaction tube 9 there is disposed an internal core 11 which in combination with the reaction tube 9 deiines an annular reaction Zone. Similarly, the extension of the injection tube 8 into the reaction tube 9 forms an annular preheat zone. The atomized and partially vaporized mixture of oil and primary steam is injected from the injection tube 8 into a concurrently moving, concentrieally disposed body of secondary steam which is fed through valved line 12 into the reaction tube 9.

The mixer 6 both mixes and atomizes and a preferred embodiment is through use of about p.s.i.g. minimum to force oil through a multihole orifice plate to form jets of oil impinging into similar jets of steam formed by a second multihole oriice plate, the yoil-steam mixture issuing from ythe holes as high velocity jets. After travel through the injection tube for from about l to 3 feet, it may be preferred to use a second orifice combination to bring about a ner state of subdivision and to reatomize coalesced oil. It is preferred to use a minimum diierential of 15 p.s.i.g. within the mixer atomizer unit regardless of the back pressure against which the mixture is delivered.

The secondary steam flows concurrently, but out of direct contact with the oil-primary steam mixture, the vatomized oil-primary steam mix-ture being within the injection tube 8 and the secondary steam being outside of the injection tube. By this means, the atomized oilprimary steam mixture is intimately and quickly admixed with the secondary steam and quickly heated by direct heat exchange of sensible heat of the secondary steam which has been heated in the upper portion of the reaction tube. Thus, the preheat zone is capable of rapidly and properly conditioning a large volume of charging stock as compared to other prior art methods.

The conditioned oil and steam are quickly passed from the injection tube 8 through the indirectly heated, annular reaction Zone Aformed between `the yinside Wall of the reaction tube 9 and the outside wall of the internal core 11. In the reaction zone, the reactants are thermally cracked and the cracked products are quenched as they leave the reaction tube 9 by quenching medium. The quenching medium is passed through line 13 and is preferably hydrocarbons produced as the result of quenching in a quench tank 14; recirculated by means of a pump 15 through -a waste-'heat boiler 16. The boiler 16 may produce steam at low pressure for use in the reaction tube 9 as secondary steam or at higher pressure for use as primary steam. It is preferred that boiler 16 produce steam at '50 to A100 p.s.i.g. in which case the 'quench oil circulated by pump 15 will normally have a temperature entering the quench tankof about 350 F. The quench oil is intimately mixed in substantial quantity vwith efliuent gas from the 'reaction tube 9, exiting normally in the range of about 1000 to about 1250 F., to cause about a 50 F. rise'in the ternperature of the quench oil. *Under these conditions,the

diluent passed through the reaction tube 9, together with hydrocarbons uncondensed in quench tank 14, pass through line 17 at about 400 to 450 F. minimum.

Additionally, secondary steam is passed or shunted through a valved line `12a and into the internal core 11 from which the steam emits from the top thereof through perforations and serves to provide a jet action to dislodge and otherwise remove any carbon tending to deposit on the top of the internal core.

The liquid product A is withdrawn from the quench tank 14 through a valved line 18 and passes through a pump 19 to a multipurpose heat exchanger 20 from which the liquid product then passes through a valved line 21 to a treater system represented by 22 wherein the treaters A, B, and C are shown. Alternatively, the liquid product A in whoie or in part may be passed through a valved line 23 through a cooler 24 from which it passes to storI age for use as fuel or as otherwise desired.

The gases and vapors from the quench tank 14 are passed through line 17 to a cooling, absorbing and/or fractionating unit represented by 25. The unit 25 may consist of one or more fractionating columns provided with suitable condensers, reflux devices, and coolers as well understood in the art. Liquid products designated B and C are withdrawn from the unit 25 through valved lines 26 and 27, respectively. The product B is an intermediate condensate and may be recycled in whole or in part into the cracking tube 9 by means of a valved line 28 which conducts the condensate from the line 26 into the mixer 6. Alternatively, product B in whole or in part 'may be passed into a second cracking or treating unit, such as treater A, through a valved line 29 'which leads to the exchanger 20. The vapors and gases which leave the to'p of the unit 25 pass through a line 30 to a cooler 31 from which gas and condensate are passed 'through line 32 to a separator 33. Any light condensate of value is passed from the separator 33 through pump 34 and line 35 to the cooling, absorbing and/ or fractionating unit represented by 25. The valueless condensate is passed from the separator 33 to drain. The product designated C is withdrawn from the unit 25 through the valved line 27 and this product is condensed steam and normally portions of light `condensate and is decanted or otherwise stripped of hydrocarbons with the residue passed to drain. A pump 36 in the valved line 27 anda valved line 37 connected thereto provides for recycle of product C to the unit 25. In like manner, a pump 38 in the valved line 28 and "a valved line 39 connected Vthereto provides 'for recycle of product B to the unit Z5. The pump 38 further provides for return of product B 'to the mixer 6 through the valved line 28 as hereinbefore described. The product designated D is withdrawn from the top of the separator 33, this product, being, for example, H2, CH4, C2H2, and oleiins, but which may contain aromatics may be passed to pressure-low temperature absorption-liquefaction equipment or to adsorption processes for gas component separation or other .processes for recovery of valuable products.

` The 'chemical and physical character of product A from quench tank 14 depends upon conditions of vthe reaction Zone. A `feed stock of carbon and hydrogen relationship CHn may 'be altered to a residual product A of relationship CH r Where r is small, for example, if n=1.8 r may only be about 0.1 to 0.4. On the other hand, substantial alteration may be brought about `and r may be about '0.6 to about 1.4. The eiiect of deeper reaction conditions is toward lower and lower values of (n-r) VWith no appreciable formation of detrimental carbon. Consequently, 'the condensables from quench tank l14,i.e., product A, are subject to a desirable wide and controlled variation, which is related to their field of use 'and to subsequent further alteration, processing and separation steps. The ycombined use of the furnacing step, the quenching Vstep `and post-treatment steps prolvde's -thereby va unique process "wherein each vstep oontributes to the alteration of the carbon-hydrogen relationship of the feed stock into -liquid products of different carbon-hydrogen relationship under high capacity unit throughput not heretofore achieved. The liquid hydrocarbons, so obtained in altered form, lare condensed hydrocarbons or hydrocarbons .absorbed in the quenching liquid in contrast to liquids not condensed from a vapor state. Within this limitation, the pressure within the reactor, exclusive of the mixer, is normally the pressure required for motivation of reactants. However, the pressure may be above atmospheric and above that required for motivation, in which case a throttle valve 40 is placed in line 17; or, if a header is used between the furnace 10 land the quench tank 14, the throttle valve is used to affect `the furnace pressure; or the throttle valve -may be so placed 'as to include the post treaters within the pressure zone.

As previously described, product A may be withidrawn lfrom the system through the valved line 23 and the cooler 24 and disposed of .as desired. However, in accordance with one preferred embodiment of the invention, product A is passed through the valved line 18 .and through the pump 19 to the multipurpose heat exchanger 20 from which it passes through the valved line .'21 to the treater system represented by 22 wherein the treaters A, B, and C are shown.

The advantages in use of treaters A, B, and C are more clearly understood by again referring to the flexible nature of furnace 1d and product A. For example, it may be elected to treat an 4oil of carbon-hydrogen relationship of .about CHM to CHL@ to the extent of a light depth of cracking `to cause a formation of gas exiting through line 17 in an amount of 5% to 20% by weight of feed stock, while subjecting the oil to substantial reaction heat to cause alteration in the chemical composition and arrangement of chemical groups as exemplified by the fact of heat absorption, nominal gas formation, all within a maximum of 0.3 second reaction time, insuicient to cause 4degrees of polymerization, and complex reformation so attendant with reactions which are permitted to proceed during longer residence time. Having found that an unexpected yield of ethylene can be produced from cuts already heavily cracked by these prior processes (particularly exemplified by U.S. Patent 2,525,276 and application Serial No. 188,567) and decidedly contrary to the teaching of the art, it is deduced that for said ethylene lto be produced, it has been preceded in earlier stages of ycracking by chemical rearrangement permitting the simple `formation of ethylene to occur from what previously was complex hydrocarbon. For example, and in relation to the foregoing, it has been found with both #2 oil and with crude oil that there is an increase of from about 20 lbs. C2H4 to about 30 lbs. of C2H4 without appreciable change in CSHS production when cracked from around about 45% depth to about 65% to 70% depth. These poundages refer to 100 lbs. of oil feed stock as a unit quantity. The finding of this relationship is new `and diiiicultly believed but proved from results of many runs made under a wide range of conditions. This proof of pretreatment effects brought about with lighter depth of cracking which apply to the condensables is susceptible of wide application. This is more apparent from the following:

Product A produced within the scope of this invention at high unit throughput rate as disclosed herein is passed to treaters A, B, and C, exemplifying known methods of treatment, such as thermal or catalytic cracking, distillation, absorption, oxidation, hydrogenation, dehydrogenation, etc., with any such steps singly or in combination. This embodiment of this invention is not concerned with such known steps as such but rather with the combination of pretreatment Within the contact time limit and other limits as defined by the appended claims with such known after-treatment step or steps to cause further alteration and/or rearrangement of chem- 6 ical constituents; Additionally, this invention does not lie in the treatment of hydrocarbons for production of valuable gases, even though these are by-products, but 'in' a new process for producing treated liquids via gas phase reaction, where in combination with the proper postor :after-treatments known in the art, there is provided a novel and efficient overall process for the production of solvents, fuels, high octane hydrocarbons and Ithe like.

It will be apparent that the process and apparatus herein disclosed for diagrammatic presentation of the invention are susceptible to numerous other possible combinations and arrangements for operation of .the invention including equipment other than that shown, such as waste heat boilers, heat exchangers, condensers, coolers, multiple fractionating columns with take-olf, and the like. However, such means have not been shown or disclosed since .they are well within the province of a person skilled in the art. Furthermore, it be `apparent that the process herein disclosed may be operated with or without the use of catalysts. In using catalyst, the catalyst to be employed may be fixed, movable, continuously movable, or fluidized, as hereinafter set forth, and these catalysts may be employed in ya simple and expedient manner relative to the preferred embodiment of the invention illustrated in Fig. l, wherein reference `symbols refer to like parts wherever they occur.

Referring now particularly to Fig. 2, a hollow internal core 50 is disposed within the reactio-n tube 9. The internal core 50 has a central portion 51 of reduced diameter which supports a catalyst mass 52 held in place by a foraminous member 53 wrapped around the central portion 51 of the internal core 50. Due to the small annular space provided between the core 50` so equipped and the reaction tube wall, the reactants in considerable measure contact the catalyst to impart catalytic eifect as desired for certain end products. ln this manner there is provided a xed catalytic surface which is exposed to the reactants and which does not impede the flow of reactants through the annular reaction zone. Accordingly, extremely high throughput is maintained. Steam from line 12a is passed into the hollow internal core 50 from which the steam emits from the top thereof through a plurality of perforations represented by 54.

In the use of catalysts, as part of this invention, wherein the catalyst is heated by radiation from. the tube Wall, and wherein the catalyst itself is a heating agent for the reactants, and wherein the catalyst may be disposed around the outer surface of a. centrally disposed internal tube or core of metal, ceramic, Carborundum or of other suitable material, said tube may be utilized advantageously, it has been discovered, as a conduit for passage of a diluent material, such as steam, countercurrent to the reactants. The diluent material can be used to control the catalyst temperature by extraction and transfer of heat from and between zones of catalyst. Furthermore, it has been discovered that there is another and very beneficial use for diluent passed through the core, particularly when the diluent is steam, wherein the steam functions as a deterrent to the formation and retention of carbon, particularly at or near the top of the core in the reaction zone. By using perforations, particularly in the top of the core, and/or around the circumference of the core, suitably spaced and sized, it is found that steam, for example, has at least two primary effects relative to carbon deposits. It lifts off and breaks up such deposits, permitting passage into a hotter zone; and provides jet action of hot steam upon carbon so deposited. By these combined effects, continuity of operation is promoted. To the end that maximum temperature of steam is desired for use in openings for passage of steam or other diluent, for beneficial effect upon carbon, or as a deterrent to carbon formation, or as an element of temperature control of reactant mixture, said steam may be passed through a conduit within the core and radiantly heated by the core.

The openings or perforations used for the passage of diluent from the core to the reactant mixture can be of any shape or size suitable for the purpose, but most conveniently are round holes of small size, for example /g to 1/fs diameter, for maximum beneficial effect upon carbon when utilizing a minimum quantity of steam passed countercurrently to the reactants passing through the reaction zone. For this purpose, there may be used only a small percentage of the total diluent passing from the tube, for example, when a 2 to 1 weight ratio of steam to hydrocarbon is used, the countercurrent steam passing through the core may amount to only about 5%. Gn the other hand, when the use is primarily as a temperature control element for either the catalyst or the reactant mixture, the steam or other diluent being passed through the core may more substantially replace the other diluent being passed concurrently into the reaction zone, but preferably the countercurrent steam will not exceed 40% of the whole. When diluents other than steam are used, there may be used materials which react with carbon and which are not solely diluents in that sense. In this category, hydrogen, and even air may be used, although with the latter, dilution with nitrogen, ue gas, etc., is safer and preferred. The core may be type 310 stainless steel, stabilized or unstabilized, but type 310 Cb is preferred except where anticatalytic action is highly desirable. In such cases, it is preferred to restrict metal Contact through use of a non-metallic exposed core surface, such as ceramic, refractory, or Carborundum types, selected according to the reaction conditions to be employed.

Referring now particularly to Fig. 3, a foraminous core 60 extends into the reaction tube 9 up through the base thereof and has its upper end terminating in the form of a foraminous funnel 61 in juxtaposition to the lower end of the injection tube 8. The core 60 is hollow and is provided with a plurality of pcrforations 62` and `is provided at its lower end with a valve 63, such as a star valve. Free-owing catalyst 64 is supplied around the injection tube 8 at the upper end of the reaction tube 9 through a valved manifold system 65 and flows downwardly within the core 60 and is discharged therefrom through the valve 63 as desired. By control of the valve 63 and valved manifold 65, the catalyst may be discharged at intervals for reactivation and replenishment or it may be continuously charged and discharged. In this manner, there is provided a movable catalytic surface exposed to the reactants or a continuously movable catalytic surface. Due to the small annular space provided between the core 69 and the reaction tube wall, the reactants in considerable measure contact the catalyst to impart catalytic effect as desired for certain end products. Accordingly, extremely high throughput is maintained with a high level of catalyst contact. Additionally, steam or other diluent may be passed by valved line 12a into and through the internal core 65) for the purpose of purging as desired.

Referring now particularly to Fig. 4, a hollow internal core 70 extends into the reaction tube 9 up through the base thereof and extends upwardly into the reaction tube to a point near the injection tube 8. Suitable catalyst 7 with fluid medium under pressure is injected into the bottom of core 70 through a pressure throttle valve line 72 and carries up through the core 7h countercurrent to the reactant stream. The catalyst emerges from the top of the core 7G into the reactant stream. and then passes downwardly therewith as a tluidized catalyst body. Suitable baffles, represented by 73, are provided for separating the catalyst from the reactant stream which passes on to the quench tank. A conduit 74 is provided for return of catalyst to the core 70. However, other suitable equipment (not shown) may be used for reactivation, replenishment, or return of catalyst to the system. The fluid medium used as a carrier for the catalyst is preferably steam but other diluent or even reactant medium may be employed for this purpose. The procedure for utilizing fluidized catalyst as set forth herein provides a simple and 8 expedient method for handling catalyst in conjunction with the other objectives of the invention.

Referring now particularly to Fig. 5, still another embodiment is shown for the effective application of countercurrent diluent. In this embodiment steam or other diluent is passed countercurrent to the reactant stream up through a hollow internal core 80. The internal core 30 has a manifold 81 in communication with the interior of the core through a plurality of pipes represented by 82.. The pipes 82 are preferably arranged in the form of a spider utilizing three pipes as support legs` to insure rigidity for the manifold 81. The manifold 81 has a plurality of perforations represented by 83 in the bottom side `thereof to project the diluent downwardly around the injection tube 8. Accordingly, when secondary steam, for example, is passed countercurrent to the reactants through core 80, the steam issues above the egress point of the injection tube 8. This causes blanketing of the entering hydrocarbon las it leaves the injection tube but yet provides for intimate mixing in the flash heat zone from which the mixture then passes through the reaction zone. The arrangement of the manifold in this manner is additionally suitable in systems where an annulus is used in lieu of an injection tube for preparing the reactants for passage through the reaction zone. However, regardless of the specic arrangement utilized, an important factor is to obtain flash heating of the reactants prior to passage through the reaction zone.

In accordance with this invention and to illustrate particularly the process for effecting cracking of hydrocarbons in a tubular furnace, the following examples are given. These examples illustrate the results obtained from the use of various type oils. In the examples, the length of the reaction tube within the furnace was approximately 25 feet of which approximately one-third constituted the preheat zone and the remainder the reaction zone. The reaction tube was 8 inches in inside diameter and the internal core was 5 inches in outside diameter and extended substantially throughout the length of the reaction zone. This gave a longitudinal annular space of 11/2 inches ywide and approximately 17 feet long for the reaction zone.

Example 1 A mixture of #2 Fuel Oil `and steam in an amount of 1748 lb. per hour tot-al and in a weight ratio of steam to oil of 1.84 passed into the reaction Zone at 580 F. gives a low yield of low molecular weight gas which expressed in terms of CZH., is 10 lb. per 100` lb. of hydrocarbon feed stock when processed under the following conditions:

A mixture of #2 Fuel Oil and `steam `in an `amount of 1720 lb. per hour total and in a weight ratio of steam to oil of 1.80 passed into the reaction reaction zone at 623 F. gives a low yield of low molecular weight gas which expressed in terms of CzH.,a is 7.71 lb. per lb. of hydrocarbon feed stock with depth of cracking 21% when processed under the following conditions:

Average reaction tube temperature F 1691 Average refractory wall temperature F 1837 Residence time of the reactants in the reaction zone seconds 0.24 Average internal core temperature j F 1239 Exit temperature of the reactants from the reaction tube F 1110 Average refractory wall temperature F 18641 At temperature between the average refractory wall temperature and the yaverage reaction tube temperature F-- 151 Residence time of the reactants in the reaction zone seconde 0.24 Average internal core temperature 1"` 1500 Exit temperature of the reactants from the reaction tube F 1140 Example 4 A mixture of #2 Fuel Oil and steam in an amount of 3050 lb. per hour total and in a weight ratio of steam to oil of 1.49 passed into the reaction zone at 872 F. gives a low yield of low molecular weight gas which expressed in terms of C2H4 is 9 1b. per 100 lb of hydrocarbon feed stock with depth of cracking 25% when processed under the following conditions:

Average reaction tube temperature F 1710 Average refractory wall temperature F 1958 Residence time of the reactants in the reaction zone seconds 0.16

Exit temperature of the reactants from the reaction tube F-- 1070 Example 5 A mixture of #2 Fuel Oi-l and steam in an amount of 4800 lb. per hour total passed into the reaction zone at 687 F. gives a low yield of low molecular weight gas which expressed in terms of C2H4 is 5 lb. per 100 lb. of hydrocarbon feed stock with ydepth of cracking 14% when processed under the following conditions:

Average reaction tubey temperature F 1760 Average lrefractory wall temperature F 2060 Residence time of the reactants in the reaction zone seconds 0.10 Exit temperature of the reactants from the reaction tube IF 1050 Example 6 A mixture of East Texas crude oil and steam in an amount of 1590 lb. per hour total and in a weight ratio of steam to oil of 1.84 passed into the reaction zone at 703 F. gives a low yield of low molecular weight gas which expressed in terms of C2H4 is 8.08 lb. per 100 lb. of hydrocarbon feed stock with depth of cracking 28% when processed under the following conditions:

Example 7 A mixture of 1408 lb. East Texas crude oil and 2440 lb. steam passed into the reaction zone at 1050 F. gives a low yield of low molecular weight gas which expressed in terms of C2H4 is less than 10 lb. per 100 lb. of hydro- '10 carbon feed stock when processed under the following? conditions:

Average reaction tube temperature F 1730 At temperature between the raverage reaction tube temperature and the average refractory wall temperature F 250 Residence time of the reactants in the reaction zone g seconds 0.11 Exit 'temperature of the' reactants from the reaction tube v ...u F Example 8 A mixture of 1408 lb. East Texas crude oil and 244-0 lb. steam passed into the reaction zone at 1050 F. gives a low yield of low molecular weight gas which expressed in terms of C2H4 is less than 18 1b. per 100 lb. of hydrocarbon feed stock with depth of cracking 40% when processed under the following conditions:

o Fb Average reaction tube temperature 2000 Average internal core tempera-ture 1690 At temperature between the average refractory wall ytemperature and the average reaction tube temperature 200 Exit temperature of the reactants from the reaction tube 1235 Example 9 East Texas crude oil, steam and ue gas in equal proportions by weight totalling 4400 lb. per hour total passed into the reaction zone in substantially complete gasified form gives a low yield of low molecular weight gas which expressed in terms of C2H4 is less than 10 lb. per 100 lb. of hydrocarbon feed stock with a depth of cracking less than 25% when processed under the following conditions:

F. Average reaction tube temperature 1878 Average refractory wall temperature 2200 Average internal core temperature 1550 Exit temperature of the reactants from the reaction Itube 1165 With reference to the above examples, it will be noted that high throughput of hydrocarbon stock exclusive of diluent, such as steam or flue gas, is accomplished in -accordance with this invention and that the cracked products lcontain a very small gas yield. In processing according to this invention the formation of C2s, CH4 and H2 is held to a minimum giving a very small gas volume in comparison to the liquid products produced which are represented by the C5s and higher.

Whereas in the foregoing examples the highest temperature of the hydrocarbon and steam mixture was 1050 F. entering the reaction zone, runs have been made at higher extrant temperature, and in the processing of residual oils, it is advantageous to use temperatures in excess of 1000 F. even with diluent steam. The combination of higher entrant temperature and a diluent to reduce hydrocarbon partial pressure has been found to be particularly advantageous in handling heavy oil. Whether its effectiveness is due to its bringing atomized oil closer to the equilibrium vapor state within the short time interval existent, whether it is due to a more effective production of reactive fog in contrast to droplets, or whether due to some other reason is not definitely known. In such cases, however, it has been found advantageous to enter the reaction zone at, for example, 1100 F., even though the desirable internal disengagement of linkages in the hydrocarbon is associated with the exit temperature which may be the same or lower than the entrant temperature to the reaction zone. Whereas the reaction may have commenced in the mixing zone when the hydrocarbon is suddenly heated to, for example, 1100 F., this zone is so close to the defined reaction A l1 zone and associated such a short time, Within it, that the expressions as made will be understood as being reasonably descriptive thereof.

In the practice of this invention, a refractory walled tubular furnace provided with an injection system for liquid hydrocarbon, such as disclosed in Reissue Patent No. 21,521 and Patent No. 2,525,276, respectively, is preferred. This combination gives remarkable flexibility in temperature control with a minimum of carbon deposition. The tubular cracking or reaction tubes are preferably disposed vertically and have a diameter of about 4 to 10 inches. Preferably the tube is in the order of 8 inches in diameter and has about 25 feet of its entire length disposed within the furnace of which about onethird of the tube length is a preheat section and two-thirds a reaction or residence time section. A type 310 stain less steel tube is suitable and this type tube with stabilizing material is preferred. The reaction tube may be lined to repress catalytic effect as desired which has heretofore been discussed in respect to the internal core which extends within the reaction tube substantially the length of the reaction section.

In accordance with this invention the hydrocarbon feed stock may be a liquid product such as a fuel oil or crude oil and may be introduced into the process with or without diluent. With steam, for example, as the diluent the ratio of steam -to hydrocarbon can be variedl to give either high or low ratios as desired depending on the diiculty encountered in vaporizing the feed stock. Normally, this ratio will be in the order of 1:10 to 5:1 with a preferred steam to hydrocarbon ratio of from about 1:1 to 3:1. The use of a diluent, such as steam, lowers the boiling point of the hydrocarbon and makes possible substantially complete vaporization of certain stocks, such as crude or topped crude, which are heavier than gas-oil, for example. Additionally, the diluent, such as steam, can be used to assist in control of the residence time which in conjunction with the control of the reaction tube wall temperature makes it possible to control the effluent temperature of the reactants within a considerable range as desired.

In the reaction section of the reaction tube the average metal wall temperature will be maintained at a temperature of at least 1685 F. with the average surface temperature of the refractory walled furnace maintained at a temperature of at least 1835 F. Under such conditions, the temperature relationship (At) between the average temperature of the reaction tube and the average surface temperature of the core will be maintained at from about 300 F. to about 600 F. While maintaining the temperature relationship (At) between the average temperature of the tube and the temperature of the cracked products emerging therefrom of at least 435 F. Higher temperatures may be employed with the upper limit primarily dictated by the materials of construction involved. Generally, it has been found that an average metal wall temperature of from about 1700 to about 2000 F. for the reaction section of the reaction tube gives very satisfactory results.

Although it is not intended that the invention shall be limited to any particular theory of operation, it appears that the components of the gaseous reactants passing through the reaction zone make multiple very short contacts with the high temperature walls of the reaction tube and the core, which contacts are believed to influence the end result in obtaining a low gas yield. This also applies to the effectiveness of the catalyst bodies disclosed herein. Thus, whereas the average temperature of the gaseous reactants may be 500 F. or more below the average tube wall temperature, it is believed that the multiplicity of these short high temperature contacts affects the end result to the extent that a certain amount of deep cracking occurs without appreciable increase in yield of gaseous end product. In other words, in refinery practice with increased depth of cracking there is almost' a conl2 tinuous increase of hydrogen to carbon ratio as the quantity of gas thus produced increases. This increase of hydrogen to carbon ratio is directly related to increased amounts of coke formed. According to the conditions of this invention and in marked contrast to the foregoing, the hydrogen-carbon ratio of the efuent gas is nearly constant even over a substantial range of cracking depth. Furthermore, the absence of substantial carbon formation according to this invention is established by lack of equivalent oxides formation in the presence of steam.

The core in its relationship to the annulus and to size of tube is a process variable. It is a factor to regulate time and plays an important part because of its own temperature, controlled on the one hand by radiant heat and on the other by extraction of heat by the reactants. Under normal operating conditions, the high surface temperatures of the reaction tube and internal core are not found to be conducive to formation of carbon or to the retention of carbon to any detrimental degree. The preferred vertical tube arrangement disclosed herein is conducive to cleanliness and freedom from operating trouble.

Whereas it has been customary in vapor phase cracking to use residence times of l to l0 secon-ds, and even with the use of diluent lsteam to limit the 4feed stock to light distillates because of coke formation, it has been found that at residence times of not more than 0.3 second the heat that normally goes into deep cracking with large yield of low molecular weight gas can be made to go into an overall much lighter depth of cracking with low yield of such gas and yet with substantial change in composi tion of the condensables. Under these conditions, the yield of CZH., may be less than 10% by weight of the hydrocarbon feed stock with an increased gain in C4s and materials of higher carbon content. This type of cracking is particularly adaptable to structural change of liquids at low gas yield preparatory to subsequent processing of the liquids formed. Another point of contrast is in the lrate of heat input per square foot of tube surface. In refinery practice, a range of from 4000 to about 20,000 B.t.u. per square foot is used wherein the latter represents very high and somewhat unusual conditions. However, in accordance with this invention, there is used from about 20,000 to about 50,000 B.t.u. per square foot in the reaction zone under which condition cracking results are quite different as has been herein set forth. Refer- :ring again `to an initial feed stock represented by a carbon to hydrogen relationship as CHLB, in accondance with the process of this invention the condensable portion of the effluent can be made to have successively lower hydrogen content substantially at will, while maintaining high throughput low residence time values. For example, reduction of the hydrogen by 10% conforms to a definite depth of cracking, 5% would be another, 15% another, and so on. Yet under each condition the vapor body would have been subjected to a temperature normally in excess of 900 F., and the compounds present would all have been subjected to a modifying temperature level. Furthermore, the depth of cracking, in terms of percent of the feed stock by weight to be converted to gas, can Vary from less than 17% -to over 40% While still maintaining high throughput and With effluent gas in the range of 900 F. to 1250 F.

The use of catalysts to inuence the purity or the composition of ultimate end products is Within the scope of this invention and includes the preferred arrangements set forth herein along with such catalysts as purnice, clays, aluminum silicates, hydrosilicates, chromium, molybdenum, lvanadium oxides, ferrie oxides, magnesia, cupric oxide, zinc oxide, potassium oxide, plus other materials and modifiers therefor as are well known in the art. Dehydrogenation is one type of reaction taking place while cracking, and butadiene is a normal constituent of the product gas. Butadiene, however, can be produced by the well-known dehydrogenation of butane or butene '13 using Well-known catalysts, and such a reaction is illustrative of the known use of catalysts and of diluents other than steam such as flue gas, nitrogen, etc., where, for example, catalyst activity might be impaired yby the' presence of steam.

It will be understood that this invention is not limited to normally liquid feed stock and that regardless of whether the feed stock is normally liquid or normally gaseous, the reactants entering the reaction zone are intended to be gaseous, as effectively as practically possible within the objectives of the invention. Once in the gaseous state, the reaction zone processing is unresponsive to any characterization of the original feed stock state as it may have existed in storage. Butane, butene, propane, land hexane are examples of feed stocks differing from oils. Such stocks are processable to utilize the high capacity features of this invention. In such cases, the liquid product A will be small in proportion to the gaseous product, thereby illustrating a process advantage which is different from the application to oil cracking per se, but which is very advantageous for the processing of blended feed stocks which heretofore have Ibeen limited in respect to capacity and performance due -to processing deficiencies.

It is evident that there are numerous factors which will inuence conditions for the most satisfactory operation of this invention, the actual limitation of which can be determined only by consideration of the starting materials and the intermediate and the finished products desired. For example, the extremely high heat inputs associated with this invention are the result of complex action. First, it demands the use of high average refractory temperatures normally above l835 F. and for high capacity throughputs in the order of 2200u to 2250 F. Second, the average metal wall temperatures for the reaction zone are normally above 1685 F. and for optimum results from about l900 to 2100 F. Third, the heat of the reacting mixture is a combination of internal radiant and convection heat under unusual temperature level relationships involving heat passage to the core, and to the gas, and from the core to the gas, all simultaneously. Fourth, the complex heat input mechanisms function simultaneously with the progressive reaction heat mechanisms. Fifth, the variants, such as preheat, dilution ratio, reactant velocity, temperature levels, core size and material, the feed stock itself, equilibrium and side reactions, catalytic effects, the diluent itself, completeness of vaporization, mixing, ash heating of hydrocarbon, surface conditions, etc., have 'direct bearing upon the high unit surface heat input of the invention. The trend in the relinery field over the years has been from lower temperature ranges upward, and with the time-temperature relationships used, the limitation of vapor phase cracking to light distillates with high hydrogen yield has given rise to the production of substantial quantities of coke which have acted to restrain progress, particularly in the field of tubular cracking. This has been contributed to by processes used in refinery practice when employing `tubular furnaces and by the limitations placed upon the maximum temperatures permissible in these furnaces. In recent nontubular refining practice, the trend has been to promote better methods of utilizing coke rather than to develop processes which avoid or greatly minimize its production.

It will be seen therefore that this invention may be carried out by the use of various modifications and changes without departing from its spirit and scope.

The advantages of the invention are as follows: a minimum of Czs, CH4 and H2 is obtained; a smaller gas yield richer in C4s and higher is obtained; a larger condensable portion which has undergone modification compared to the feed stock is obtained; and the compounds present in the liquid portion are represented in part by the aromatic and olefin series and some are, of course,

naphthenic, andvaluablevantiknock compounds are obf tained therewith.

This application is a continuation-in-part of myl copending application fory United States Letters Patent, Serial No. 188,567, filed October 5, 1950, now abandoned.

What I claim and desire to protect by Letters Patent is:

1. In the process of converting hydrocarbons to obtain high capacity throughput rper unit of transverse crosssectional gas passage area with high yield of liquid products and low yield of. gaseous products containing less than 18 pounds of ethylene per 100. pounds of hydrocarbon feed stock in a tubular furnace whereby the converted end products are recovered therefrom and separated, the improvement which comprises passing a reactant mixture comprising heated diluent gas and gaseous hydrocarbon through the reaction zone of an elongated metallic reaction tube for a period of not more than 0.3 second residence time in said zone and at high capacity 4throughputgof the reactants while supplying external heat to the reaction zone at an average rate of more than about 20,000 B.t.u. per square foot of reaction tube surface to maintain an average temperature of the tube at the reaction zone of from about 1335 to about 2l00 F., and controlling the relationship between said throughput and said average temperature of the tube to maintain a temperature differential (At) of at least 435 F. between the said average temperature of the tube and the reacted products immediately emerging from the reaction zone thereof and to maintain said reacted products at a temperature of from about 900 to about 1665 F. upon emergence from said reaction zone, whereby there is obtained after recovery and separation of the said reacted products the aforesaid high yield of liquid products and low yield of gaseous products.

2. In the process of converting hydrocarbons to obtain high capacity throughput per unit of transverse crosssectional gas passage area with high yield of liquid products and low yield of gaseous products containing less than 18 pounds of ethylene per l00 pounds of hydrocarbon-feed stock in a tubular furnace whereby the converted end products are recovered therefrom and separated, the improvement which comprises passing a reactant mixture comprising heated diluent gas and gaseous hydrocarbon through the reaction zone of an elongated metallic reaction tube for a period of not more than 0.3 second residence time in said zone and at high capacity throughput of the reactants while supplying external heat to the reaction zone at an average rate of more than about 20,000 B.t.u. per square foot of reaction tube surface to maintain an average temperature of the tube at the reaction zone of from about 1335 to about 2l00 F., -the said reaction zone being formed by an elongated core disposed within the elongated reaction tube to Aform a narrow substantially annular passageway for the `reactants between said core and said tube, and controlling the relationship between said throughput and said average temperature of the tube to maintain a temperature differential (At) of at least 435 F. between the said average temperature of the tube and the reacted products immediately emerging from the reaction zone thereof and to maintain said reacted products at a temperature of from about 900 to about l665 F. upon emergence from said reaction zone, whereby there is obtained after recovery and separation of the said reacted products the aforesaid high yield of liquid products and low yielid of gaseous products.

3. The process of claim 2 wherein the diluent gas and the gaseous hydrocarbon are passed through lthe reaction zone as a mixture comprising steam and vaporized hydrocarbon oil, respectively.

4. The process of claim 2 wherein the reactants comprise steam, vaporized hydrocarbon oil and catalyst.

5. The process of claim 2 wherein diluent gas is passed through the elongated core countercurrent to the reactant gaseous hydrocarbon l'115 mixture and `emerges therefrom and is then passed concurrent with said mixture.

6. The processof claim 2 wherein diluentgas is passed through the elongated core countercurrent to the .gaseous hydrocarbon and is emerged beyond 'the entrance of said gaseous hydrocarbon into the reaction zone and is 'then passed concurrent ywith the saidv gaseous hydrocarbon.

7. The -process of claim 2 wherein the average surface temperature of the core is maintained at a temperature of -from about 300 to about 600 F. below the average temperature of the tube at the reaction zone.

48. In the processof converting hydrocarbons to obtain high capacity throughput -per unit of transverse crosssectional gas passage area with high yield of liquid yproducts and low yield of Igaseous Yproducts `containing 'less than 18 poundsof ethylene per 100 pounds of hydrocarbon vfeed stock in -a Vtubular furnace whereby the converted end products are recovered therefrom and separated, the improvement vwhich comprises passing a reactant mixture comprising heated diluent gas 'and through the reaction zone of an elongated metallic reaction tube for a period of not more than 0.3 second residence Vtime in said zone and at high capacity Vthroughput of the reactants while supplying externa'lfheatto the 'reaction Zone at an average rate of more than about 20,000 B.t.u. per square ffoot vof -reaction tube surface to 'maintain an average temperature of the tube at the reaction zone of from about l1335" to about 2100 F., the said reaction zone vbeing -formed by an elongated tubular core disposed within the elongated reactiontube to form anarrow substantially lannular passageway for the reactants between said core and vsaid tube and said core containing catalyst 'for contact of the reactants therewith, and controlling lthe relationship between 'said A'throughput and said average 'temperature of the .tube lto maintain a temperature 'differential (Ar) of latleast 435 F. between lthe said average temperature o'f the tube-and the reacted'products 'immediately emerging -tfrom the Yreaction Zone thereof and to Amaintain said yreacted products at la temperature '1"6 of from about 900 to about I1665 1F. Vupon emergence from said reaction Zone, whereby there is obtained after recovery and separation of the said reacted products the aforesaid high yield of liquid products and low yield of gaseous products.

9. The process of claim 8 wherein the :elongated tubular core contains an external 'catalyst mass .exposed to the'reactants.

l0. The process of claim 8 `wherein fluidized catalyst is passed through the elongated tubular core .countercurrent to the reactants and emerges therefrom and is then -passed concurrent with said reactants through Vthe reaction zone.

11. The process of claim 8 wherein 'the `elongated tubular Acore is perforated vand has a catalytic ibody therein exposed to the reactants.

12. The process of claim 8 wherein fthe elongated tubular core is perforated and has a lmovable catalytic body therein exposed to the reactants.

'13. The process of claim 8 wherein the elongated tubular core is perforated and has a continuously movable catalytic'body therein exposed tothe reactants.

References Cited in the le of this patent -UNITED STATES APATENTS 11,351,859 Lowe et al. Sept. 7, 1920 1,642,624 Northrup Sept. A13, 1927 2,236,535 Hasche Apr. -1, 19411 2,283,643 Nagel May 19, 1942 2,288,395 Ellis 'June 30, 1942 2,311,984 Guild Feb. 23, 1943 2,326,438 Clarke Aug. Z10, 1943 2,525,276 Shaplcigh Oct. 10, -195.0 2,629,684- Leffer Feb. 24, y19,53

OTHER REFERENCES Nelson: 'Petroleum Rening Engineering, pp. 58.1 :to 586 (-pages), June 28, 1949. 

2. IN THE PROCESS OF COVERING HYDROCARBONS TO OBTAIN HIGH CAPACITY THROUGHOUT PER UNIT OF TRANSVERSE CROSSSECTIONAL GAS PASSAGE AREA WITH HIGH YIELD OF LIQUID PRODUCTS AND LOW YIELD OF GASEOUS PRODUCTS CONTAINING LESS THAN 18 POUNDS OF ETHYLENE PER 100 POUNDS OF HYDROCARBON FEED STOCK IN A TUBULAR FURNACE WHEREBY THE CONVERTED END PRODUCTS ARE RECOVERED THEREFROM AND SEPARATED, THE IMPROVEMENT WHICH COMPRISES PASSING A REACTANT MIXTURE COMPRISING HEATED DILUENT GAS AND GASEOUS HYDROCARBON THROUGH THE REACTION ZONE OF AN ELONGATED METALLIC REACTION TUBE FOR A PERIOD OF NOT MORE THAN 0.3 SECOND RESIDENCE TIME IN SAID ZONE AND AT HIGH CAPACITY THROUGHPUT OF THE REACTANTS WHILE SUPPLYING EXTERNAL HEAT TO THE REACTION ZONE AT AN AVERAGE RATE OF MORE THAN ABOUT 20,000 B.T.U. PER SQUARE FOOT OF REACTION TUBE SURFACE TO MAINTAIN AN AVERAGE TEMPERATURE OF THE TUBE AT THE REACTION ZONE OF FROM ABOUT 1335* TO ABOUT 2100* F., THE SAID REACTION ZONE BEING FORMED BY AN ELONGATED CORE DISPOSED WITHIN THE ELONGATED REACTION TUBE TO FORM A NARROW SUBSTANTIALLY ANNULAR PASSAGEWAY FOR THE REACTANTS BETWEEN SAID CORE AND SAID TUBE, AND CONTROLLING THE RELATIONSHIP BETWEEN SAID THROUGHOUT AND SAID AVERAGE TEMPERATURE OF THE TUBE TO MAINTAIN A TEMPERATURE DIFFERENTIAL ($) OF AT LEAST 435* F. BETWEEN THE SAID AVERAGE TEMPERATURE OF THE TUBE AND THE REACTED PRODUCTS IMMEDIATELY EMERGING FROM THE REACTION ZONE THEREOF AND TO MAINTAIN SAID REACTED PRODUCTS AT A TEMPERATURE OF FROM ABOUT 900* TO ABOUT 1665* F. UPON EMERGENCE FROM SAID REACTION ZONE, WHEREBY THERE IS OBTAINED AFTER RECOVERY AND SEPARATING OF THE SAID REACTED PRODUCTS THE AFORESAID HIGH YIELD OF LIQUID PRODUCTS AND LOW YIELD OF GASEOUS PRODUCTS.
 3. THE PROCESS OF CLAIM 2 WHEREIN THE DILUENT GAS AND THE GASEOUS HYDROCARBON ARE PASSED THROUGH THE RACTION ZONE AS A MIXTURE COMPRISING STEAM AND VAPORIZED HYDROCARBON OIL, RESPECTIVELY. 